Prestressed structure

ABSTRACT

In a prestressed structure for forming roofs or the like, a plurality of elongated curved members are arranged in side by side relationship to each other, their opposite ends are attached to the corresponding ends of adjacent members and their longitudinal edges are spaced from each other to define a gap. The curvature of the members is reduced by drawing the adjacent spaced edges of the members together so as to close the gap to effect prestress forces in said members.

United States Patent Schenk 154] PRESTRESSED STRUCTURE [72] Inventor: Robert E. Schenlt, Waterloo, Iowa [73] Assignee: Schenk Engineering Co.

[22] Filed: May 18, 1970 [21] Appl. No.: 38,373

Related US. Application Data [63] Continuation-impart of Ser. No. 790,214, Jan. 10,

1969, abandoned.

[52] US. Cl. ..52/82, 52/222, 52/584 [51] Int. Cl. ..E04b 7/10, 1504b 7/00 [58] Field of Search ..52/748, 741, 80, 82, 222, 223,

[56] References Cited UNITED STATES PATENTS Wiggins ..52/82 X 1 May 9, 11972 2,820,990 1/1958 Johnson "287/2092 2,910,018 10/ 1 959 Rothfuchs et a1 ..52/748 3,176,845 4/1965 Schenk ..210/150 3,394,508 7/1968 Burke, Jr. ..52/82 3,449,884 6/1969 Joor ..52/82 X 3,473,272 10/1969 Hasselquist ..,...52/222 X Primary Evaminer-Frank L. Abbott Assistant ExamIner-Henry E. Raduazo I Attorney-Molinare, Allegretti, Newitt & Witcoff [57] ABSTRACT In a prestressed structure for forming roofs or the like, a plurality of elongated curved members are arranged in side by side relationship to each other, their opposite ends are attached to the corresponding ends of adjacent members and their longitudinal edges are spaced from each other to define a gap. The curvature of the members is reduced by drawing the adjacent spaced edges of the memberst'ogether so as to close the gap to effect prestress forces in said members.

13 Claims, 6 Drawing figures l PATENTEDMAY 9 I972 SHEET 1 OF 2 IN\ LN/Uly ROBERT E. SCHE/VK ATTORNEYS PATENTEDHAY 9|972 3,660,953

7 sum 2 ur 2 34 30 R08ERT E. SCHE/VK .4 m, 1 Meflfl ATTORNEYS PRESTRESSED STRUCTURE RELATED APPLICATIONS BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to a prestressed structure and, more particularly, to a roof construction which is prestressed and a method of prestressing the construction.

In various structure constructions, and particularly in roofs, it is frequently desirable to prestress the roof in such a manner as to at least partially support the weight of the roof material and reduce the probability of collapse due to wind forces, weight of accumulated snow, and other forces to which the structure is subjected in use. Such prestressing is frequently accomplished at the site of manufacture of the various structural components of the roof, the various components being delivered to the installation site in an already prestressed condition. Such prefabricated prestressing generally necessitates elaborate provisions to insure that the final construction components as received at the site of installation are both stressed in the proper manner and are of uniform dimensional quality such that the components will properly fit together when the components are being assembled.

The prestressed structure of the invention is both simple to manufacture and assemble and a finally assembled structure is provided in which internal prestress forces act to offset the weight of the structure and other variable forces to which the structure might be subjected during use, such as accumulated snow. The structure of the invention may be rapidly, easily and inexpensively prestressed at the site of installation as the structure is being constructed, the components of the structure being manufactured and delivered to the installation site in substantially unprestressed form, reducing the probability of misfit at the site of installation and enabling selection of the degree of prestress at the time of installation. In one form of the invention, a simple channel member may be provided for rapidly and easily effecting prestress of the structure at the site of installation. The prestressed structure of the invention is both simple and inexpensive to manufacture and may be readily installed with a minimum of tools. The prestressing principles of the invention may be readily employed in the construction of roofs. When practicing the principles of the invention, a substantial number of different materials, including polymeric materials such as fiberglass which may provide heat and light to the interior of the structure from solar rays, may be employed to form the structure or roof. In a prestressed roof which is constructed in accordance with the principles of the invention, the number of various components which are necessary in the construction may be minimized and a roof may be provided which is substantially self-supporting, obviating the need for extensive ancillary supporting structures to support the roof in its finally installed position.

In one principal aspect, the method of forming the prestressed structure of the invention comprises providing a plurality of elongated members each of which has a planar portion which is curved over a major portion of its length. At least a pair of the curved members are positioned in side by side relationship such that their adjacent edges are proximate each other at longitudinally spaced points and are spaced from each other between the points to define a gap. The curvature of the planar portions is then reduced by drawing the spaced edges together to close the gap, whereby stress forces are effected in the planar portions.

In another principal aspect, the structure of my invention comprises a plurality of elongated members which are arranged in side by side relationship in which the edges of each of the members are normally spaced from each other to define a gap and in which each of the members includes a planar portion which is curved over a major portion of its length to normally define a given curvature. Stressing means comprises fastening means which fastens the adjacent spaced edges of the members to close the gap and reduce the given curvature to effect prestress forces in the planar portions.

These and other objects, features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS In the course of this description, reference will be frequently made to the attached drawing in which:

FIG. I is an overall view of a first preferred embodiment of prestressed roof constructed in accordance with the principles of the invention;

FIG. 2 is an elevation view of the roof panels before and after prestressing as viewed substantially along line M-M of FIG. 1;

FIG. 3 is an enlarged cross-sectioned elevation view taken substantially along line 3-3 of FIG. 1;

FIG. 4 is a broken view of a second preferred embodiment of roof constructed in accordance with the principles of the invention in which the prestressed members form a frame for the roof;

FIG. 5 is a broken perspective view of still another embodiment of roof constructed in accordance with the principles of the invention, in which a channel member is shown for fastening and prestressing the roof panels; and

FIG. 6 is an enlarged cross-sectioned elevation view taken substantially along line 6-6 of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1-3, a first preferred embodiment of roof constructed in accordance with the principles of the invention is shown. The roof 10 shown is of the type having a generally concave exterior surface and an overall shape which is substantially frustoconical in form including a base 12 which is adapted to be mounted on the building or other foundation structure S which is to be covered. By way of example, such structure may be a filter bed and the roof, in addition to preventing snow and the like from entering the filter bed, may be open at the top 13 and provide the functions described in my U.S. Pat. No. 3,176,845, granted Apr. 6, 1965. It should be understood however, that the prestressed structure of the present invention is not limited to use only as a roof or as a roof for such filter beds, but is capable of use in the construction of a wide variety of structures.

The roof 10 includes a plurality of generally trapezoidal arcuate panels 14, I4, 14", and 14. Unless specific individual ones of the panels are being described, the panels hereafter will be described in terms of panel 14 since each of the individual panels shown are identical. The lower end 16 of each of the panels 14 is substantially wider than the upper end 18 so as to form the overall frustoconical roof when installed. Each of the panels 14, in its unprestressed state, has an overall shape such that the generatrix of the surface is a straight line that remains parallel to its previous position as it is longitudinally translated along an arc to define the surface of the panel. Each of the panels 14 is formed from a somewhat resilient material, such as sheet metal or various synthetic polymeric materials including fiberglass and the like. Each panel comprises a planar web portion 20 which is of substantial width, and a pair of upstanding flanges 21 and 22 formed integrally with the web portion and extending longitudinally along its longitudinal edges. As initially formed, each of the panels is substantially unprestressed, the planar portions 20 being generally arcuate in cross section and both the planar portion 20 and edge flanges 21 and 22 having a given initial curvature.

In order to clearly set forth the principles of the invention, a description of the manner of construction and prestressing the roof follows. Referring to FIG. I, a plurality of the panels I4, l4, I4", 14'' are arranged in side by side relationship and the top ends 18 of the panels are elevated to the position shown. While the top ends are held in the elevated position, the panels, for example 14 and 14', are moved so that the edges of the bottom ends 16 and the top ends 18 of the adjacent panels touch each other and, preferably are attached together at points 17 and 19, respectively. The method used to elevate and hold the panels in the elevated position may be one of several well known methods, such as suspension from a crane or from a centerpole construction. The method of elevating the panels will not be described herein, since it forms no part of the present invention and the selection of a suitable method may be readily made by one skilled in the art.

Due to the longitudinal curvature and shape of each panel 14, when the ends of adjacent panels are mated with each other at points 17 and 19, a gap G obtains between the longitudinal edge flanges 21 and 22 of the adjacent panels, the gap extending longitudinally between the points 17 and 19 along a meridian generally indicated by line M-M. As shown in FIG. 1, all of the panels of the roof have been located in their final position and prestressed, with the exception of the last two panels 14 and 14, the positioning and prestressing of which will now be described.

The cross-sectional curvature of the adjacent panels proximate the gap G and prior to prestressing, is shown in FIG. 2 in the dot and dash lines. It will be seen that, prior to final positioning, the curvature of the web or planar portion 20, as well as of the longitudinal edges 21 and 22 of the panels, is somewhat greater than the curvature of the panels after they are finally positioned, the planar portion 20 and panel edge 22 after positioning being shown in the solid lines of FIGS. 2. To finally position and prestress these last panels, the longitudinal edges 21 and 22 of the adjacent panels 14 and 14 are drawn together over their length from the dot and dash position to the solid position shown in FIG. 3 in such a manner as to close the gap G between the panels. When such gap closing force is exerted on the resilient panels, the panels will be somewhat deformed as shown in FIGS. 2 and 3 and the curvature of both the panel edges and the planar portions will tend to be reduced or become straighter as shown in the solid lines of FIG. 2. Such deformation will cause a given point P1 on the panel edge to move from a given latitude L1 upward and outward to a point F2 on a new higher latitude L2. When the curvature of the panels is reduced in this manner, tension forces 81 will be induced in the outer concave face material of the panel and compression forces S2 will be induced in the inner convex face material. These resulting internal stress components S1 and S2 in the panel material are exerted in opposite parallel directions toward and away from points 17 and 19 of the panel respectively. Since S1 and S2 are spaced slightly from each other, a couple is produced by these tension and compression forces which has a stress component S3 which is exerted in an upward vertical direction at P2. Although a single component S3 is shown, it will be understood that forces will act upward in varying degree over the entire length of the panel due to the deformation of the panel over its length.

After the gap G has been so closed by drawing the panel flanges together, longitudinal upturned flange 21 of panel 14 is fastened to the corresponding adjacent longitudinal flange 22 of the next adjacent panel 14. The fastening may be accomplished by way of bolts 26, as shown in FIG. 3, or by way of a slideable channel member which will be described later. The panels thus will be held in their deformed somewhat straightened stressed position.

It will be seen that the direction in which the stress forces 51, S2 and S3 are exerted tend to counterbalance the weight of the panels themselves, as well as any downward forces caused by snow accumulation and the like. The existence of such stress forces enables a substantial reduction in the need for various ancillary support beams, posts and the like and, in fact, in most installations a center pole is unnecessary as shown in FIG. 1 since the panels are self supporting. It will also be apparent that the panels 14 not only act as support structure for the roof but also provide the skin of the roofas well,

substantially reducing the number of various components which are necessary to complete the final roof structure.

Although it is preferred that all or at least the major part of the number of panels be positioned and mated at respective points 17 and 19 prior to prestressing, it will be understood that panels may be both positioned and prestressed one by one prior to the positioning of the next adjacent panel.

Referring to FIG. 4, a second embodiment of the invention is shown wherein the principles of the invention are utilized to form a prestressed supporting frame for the roof and the surface plates or skin of the roof may be installed separately. In this embodiment, the prestressed members take the form of generally V-shaped elongated arcuate angles 30 each of which has a flange 32 which is substantially similar to the upturned flanges 21 and 22 and a flange 34 extending outward at a substantial angle from flange 32. Flange 34, in effect, forms a planar portion which is comparable to the web portion 20 in the previously described embodiment.

To construct the frame, each of the ends of the V-shaped angles 30 is attached to the corresponding ends of the adjacent angle, a gap obtaining between flanges 32 over their length similar to the gap G previously described. The angles are then drawn together to close the gap as previously described with respect to the plates 14 of FIG. 1, and the flanges 32 of adjacent ones of the angles are fastened together. A frame structure is thus formed in which the flanges 34 are prestressed in the manner previously described. After the frame has been formed and prestressed, individual skin sheets 36 may be attached between flange 34 of one prestressed angle and the next adjacent angle by suitable fastening means, such as bolts 38.

Referring now to FIGS. 5 and 6, a channel member embodiment is shown in which a channel member 40 may be utilized to both draw the edges of the panels 42 together with a zipperlike action to prestress the panels and to fasten these edges together in their prestressed curvature. In this embodiment, each of the panels 42 is substantially identical in construction to the panels 14 previously described, except that the upturned edge flanges 21 and 22 are further flanged at the top 44.

The elongated channel member 40 is substantially C-shaped in cross-section and comprises a web portion 46 having a pair of longitudinally extending flanges 48 extending downward from each side and a pair of flanges 50 extending inward from flanges 48 in spaced relation to the underside of the web portion 46. The flanges 50 are spaced from the web portion 46 by a distance substantially equal to the thickness of the top flanges 44 and flanges 48 are spaced from each other by a distance substantially equal to twice the width of each flange 44, whereby the flanges 44 are snuggly received in the channel member. The channel member 40 may be more or less curved depending upon the combined resiliency of the panels 42 and the channel members, such that when the channel members are fully slid onto the flanges 44, the final prestressed curvature results.

In order to prestress the panels 42, the panels are positioned in side by side relationship with their ends mated at points 17 and 19, as previously described with respect to FIG. 1. Although not absolutely necessary, the adjacent panels are preferably attached together at points 17 and 19 prior to the positioning of member 40. Channel member 40 is then slid over one end of the flanges 44 and is progressively slid over the length of the flanges as shown in FIG. 5. As sliding movement of the channel member 40 progresses, the flanges 21 and 22 are drawn together so as to progressively close the gap G. As the gap is being closed, the original curvature of the planar portions 20 of each of the panels as well as the flanges 21 and 22 will be reduced, prestressing the panels as previously described.

It will be appreciated that, in addition to drawing the panels together to achieve the desired prestress, the channel members 40 also fasten the panels together in their final prestressed condition. If desired, bolts or other fastening means in addition to channel members 40 may also be provided to attach flanges 21 and 22 together.

Moreover, although the channel members 40 have been shown and described as being employed in the prestressing and fastening of the full plate embodiment, they may also be readily employed in the construction of a frame embodiment similar to that shown in FIG. 4.

It will be understood that although a roof construction has been shown which is substantially frustoconical in shape and circular in cross-section, other shapes and cross-sections may be formed when practicing the principles of the invention.

It should also be understood that the embodiments of the present invention which have been described are merely illustrative of a few of the applications of the principles of the invention. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention.

What is claimed is:

1. A method of forming a prestressed structure comprising:

providing a plurality of elongated members each of which includes a planar portion defined by side edges and end edges extending between said side edges, said planar portion being curved over a major part of the length of said members so as to normally define a given curvature which is substantially arcuate in longitudinal cross section,

positioning at least a pair of said curved members in side by side relationship such that the adjacent side edges of said pair of members are proximate each other at longitudinally spaced points and are spaced from each other between said points to define a gap extending between said points,

reducing said curvature of the planar portions'of said members by drawing said spaced side edges together to close said gap while maintaining the end edges in a fixed relationship to each other, the reduction in said curvature over the length of said members effecting stress forces in the planar portion of said pair of members.

2. The method of claim 1 wherein said spaced proximate the opposite end edges of said members.

3. The method of claim 1 wherein said pair of members are firmly attached together at said spaced points and the side edges are then drawn progressively together from one of said points to the other to reduce the curvature of said members.

4. The method of claim 1 wherein said side edges are drawn together by progressively sliding a cap member from one of said points to the other.

5. In a prestressed structure,

a plurality of elongated members arranged in side by side relationship to each other and each having a planar portion defined by end edges and side edges, adjacent ones of said side edges abutting at longitudinally spaced locations points are and being normally spaced from each other so as to define a gap between said locations, said planar portion being curved over a major portion of its length so as to normally define a given curvature which is substantially arcuate in longitudinal cross section,

means for maintaining said end edges in fixed relationship to each other, and

means for stressing said planar portions comprising fastening means which fasten the adjacent spaced edges of said members together over their length such that said gap is closed and said given curvature is reduced, whereby prestress forces are effected in said planar portions.

6. In the prestressed structure of claim 5, wherein said side edges comprise flanges extending from said planar portions and said stressing means comprise elongated channel means slidably positioned over the adjacent flanges of adjacent ones of said members and drawing said adjacent flanges together over their length.

7. In the prestressed structure of claim 5, wherein the concave surface of said curved planar portion is stressed in tension and the convex surface of said curved planar portion is stressed in compression when said curvature is reduced.

8. In the prestressed structure of claim 5, wherein said structure is substantially circular in horizontal cross section and the exterior surface of the structure is concave.

9. In the prestressed structure of claim 5, wherein said structure is substantially frustoconical.

10. In the prestressed structure of claim 5, wherein said members comprise curved sheets of flexible material each having a web portion of substantial width and an upturned flange extending along each longitudinal edge thereof, and said stressing means comprises fastening means which fastens a flange of one sheet with an adjacent flange of an adjacent sheet, said web portion of each of said sheets forming the surface of said structure.

11. In the prestressed structure of claim 10, wherein said sheets are formed of a polymeric material.

12. In the prestressed structure of claim 5, wherein said members comprise generally V-shaped curved angles each having a first flange and a second flange extending at an angle to the first flange, and said stressing means comprises fastening means which fastens adjacent first flanges of adjacent ones of said angles together to close the gap therebetween, said planar portions comprising said second flanges of said adjacent angles which extend in opposite directions from each other and are adapted to carry the surface panels of said structure thereon, said fastened angles forming a prestressed support frame for said structure.

13. In the prestressed structure of claim 5, wherein said structure is a roof. 

1. A method of forming a prestressed structure comprising: providing a plurality of elongated members each of which includes a planar portion defined by side edges and end edges extending between said side edges, said planar portion being curved over a major part of the length of said members so as to normally define a given curvature which is substantially arcuate in longitudinal cross section, positioning at least a pair of said curved members in side by side relationship such that the adjacent side edges of said pair of members are proximate each other at longitudinally spaced points and are spaced from each other between said points to define a gap extending between said points, reducing said curvature of the planar portions of said members by drawing said spaced side edges together to close said gap while maintaining the end edges in a fixed relationship to each other, the reduction in said curvature over the length of said members effecting stress forces in the planar portion of said pair of members.
 2. The method of claim 1 wherein said spaced points are proximate the opposite end edges of said members.
 3. The method oF claim 1 wherein said pair of members are firmly attached together at said spaced points and the side edges are then drawn progressively together from one of said points to the other to reduce the curvature of said members.
 4. The method of claim 1 wherein said side edges are drawn together by progressively sliding a cap member from one of said points to the other.
 5. In a prestressed structure, a plurality of elongated members arranged in side by side relationship to each other and each having a planar portion defined by end edges and side edges, adjacent ones of said side edges abutting at longitudinally spaced locations and being normally spaced from each other so as to define a gap between said locations, said planar portion being curved over a major portion of its length so as to normally define a given curvature which is substantially arcuate in longitudinal cross section, means for maintaining said end edges in fixed relationship to each other, and means for stressing said planar portions comprising fastening means which fasten the adjacent spaced edges of said members together over their length such that said gap is closed and said given curvature is reduced, whereby prestress forces are effected in said planar portions.
 6. In the prestressed structure of claim 5, wherein said side edges comprise flanges extending from said planar portions and said stressing means comprise elongated channel means slidably positioned over the adjacent flanges of adjacent ones of said members and drawing said adjacent flanges together over their length.
 7. In the prestressed structure of claim 5, wherein the concave surface of said curved planar portion is stressed in tension and the convex surface of said curved planar portion is stressed in compression when said curvature is reduced.
 8. In the prestressed structure of claim 5, wherein said structure is substantially circular in horizontal cross section and the exterior surface of the structure is concave.
 9. In the prestressed structure of claim 5, wherein said structure is substantially frustoconical.
 10. In the prestressed structure of claim 5, wherein said members comprise curved sheets of flexible material each having a web portion of substantial width and an upturned flange extending along each longitudinal edge thereof, and said stressing means comprises fastening means which fastens a flange of one sheet with an adjacent flange of an adjacent sheet, said web portion of each of said sheets forming the surface of said structure.
 11. In the prestressed structure of claim 10, wherein said sheets are formed of a polymeric material.
 12. In the prestressed structure of claim 5, wherein said members comprise generally V-shaped curved angles each having a first flange and a second flange extending at an angle to the first flange, and said stressing means comprises fastening means which fastens adjacent first flanges of adjacent ones of said angles together to close the gap therebetween, said planar portions comprising said second flanges of said adjacent angles which extend in opposite directions from each other and are adapted to carry the surface panels of said structure thereon, said fastened angles forming a prestressed support frame for said structure.
 13. In the prestressed structure of claim 5, wherein said structure is a roof. 